A method of the type described in the opening paragraph is known as such, for example from the U.S. Pat. No. 8,440,860 B2, granted in the name of the present applicant. More particularly, this document discloses a method in which solid lactide is mixed with anhydrous dimethylamine at room temperature. The examples show that substantial conversion of the lactide into N,N-dimethyllactamide could only be achieved at high temperature and prolonged reaction times. Thus, a concentration of about 85% N,N-dimethyllactamide was obtained in the reaction mixture after a reaction time of 4 hours at 103° C. Under these conditions, degradation of the reaction product may be expected. In view of this, the overall efficiency of this process is relatively low. Moreover, the optical purity of the desired reaction product may decrease due to occurrence of racemization within the lactate-part of the produced N,N-dimethyllactamide. Preliminary experiments have shown that such racemization is even more pronounced in the production of N,N-diethyllactamide under the conditions disclosed in the cited patent document.
A similar method is known from the USA patent document with grant number U.S. Pat. No. 2,539,473. This patent document describes a method of producing N,N-diethyllactamide whereby lactic acid oligomer compound having a degree of polymerization of about 11 is refluxed with diethylamine at high temperatures for more than 40 hours in order to obtain a substantial amount of N,N-diethyllactamide. Again, these conditions promote the formation of degradation products originating from the desired N,N-diethyllactamide as well as extensive racemization.